The present invention concerns a circuit arrangement for controlling a rotary-magnet measuring instrument by an input voltage via a controlled source of current, the arrangement comprising a first amplifier with a first negative-feedback resistor and a first resistor.
Ammeters which are developed as rotary-magnet measuring instruments generally have a non-linear course of their characteristic curve, and their display characteristic. The course can be defined as approximately S-shaped. For the reliable and rapid reading of such rotary-magnet measuring instruments, however, a linear course of the characteristic curve is generally desirable.
If in known circuit arrangements of the aforementioned type the rotary-magnet measuring instrument is fed from a source of current which is fed by an input voltage--a measurement voltage or a voltage derived therefrom--the said non-linear relationship between the input voltage and the deflection of the pointer of the rotary-magnet measuring instrument is retained if the amplifier, as active part of the source of current, is connected in conventional manner to a first negative-feedback resistor and a first input resistor. The negative-feedback resistor and the first input resistor form a linear characteristic curve of the source of current.
In order to compensate for the non-linearity of the characteristic curve of the rotary-magnet measuring instrument, a non-linearly acting network developed, for instance, with diodes could be connected in front of the said rotary-magnet measuring instrument or source of current. However, such networks are relatively expensive if the points of differing slope of the characteristic curve are to be precisely defined and constant, particularly as a function of the temperature. As a result, the possibilities for the use of such networks are limited, particularly in the field of automobile instrument panels.